Usually, hydrosilylation-curable organopolysiloxane compositions have poor adhesion to substrates made from materials such as metals, organic resins, and especially from thermoplastic resins. Therefore, it was proposed to use an adhesion-promoting agent or a curable organopolysiloxane composition that contains an agent which is composed of an organopolysiloxane which has in its molecule a silicon atom bonded to an epoxy-containing organic group, an alkoxy group, an alkenyl group, or a univalent hydrocarbon group other than an alkenyl group (see Japanese Unexamined Patent Application Publications (hereinafter referred to as “Kokai”) S64-85224). Other adhesion-promoting agents and curable organopolysiloxane compositions that contain aforementioned adhesion-promoting agents that comprise an organopolysiloxane having silicon-bonded alkoxy groups, alkenyl groups, or alkyl groups are disclosed in Kokai H04-11634, H04-178461 and H06-145525. Kokai 2005-105217 discloses a curable organopolysiloxane composition which is intended for sealing semiconductor elements and which consists of a linear-chained organopolysiloxane having alkenyl and aryl groups, a branch-chained organopolysiloxane having alkenyl and aryl groups, an organopolysiloxane having silicon-bonded hydrogen atoms and aryl groups, and a hydrosilylation catalyst. In other words, it is shown that adhesion-promoting agents that comprise organopolysiloxanes that contain epoxy-containing organic groups, alkoxy groups, alkenyl groups, and alkyl groups are known.
However, when the aforementioned curable organopolysiloxane compositions are used for adhesively connecting parts to substrates by thermal curing, in particular, to substrates made from metal, or organic resins, and especially to thermoplastic resins that have polar bonds, then, even at the initial stage of a thermal cycle the connected parts are subject to peeling from the substrate at the interface with the latter. Therefore, the use of such curable organopolysiloxanes for sealing semiconductor elements may reduce reliability of respective semiconductor devices.
It is an object of the present invention to provide a novel adhesion-promoting agent, a curable organopolysiloxane composition that contains the aforementioned adhesion-promoting agent and that possesses excellent adhesion to organic-resin substrates or the like, and is suitable for the formation of a cured body of high refractive index and high optical transmissivity. It is another object of the invention to provide a semiconductor device that uses the aforementioned composition and is characterized by high reliability.